Adding More Panels to a Sunny Boy Inverter

[Softco]

Because of State, Fed etc. incentives I can get a 5-panel professional install virtually for free, but each additional panel adds significantly to the cost after that, when also professionally installed.

I see that panels themselves are not nearly as expensive when purchased w/o install. Is there a reason why I shouldn't have the 5 panels professionally installed, and then tie in additional panels later that I install myself? I've read that adding panels is very easy to do with micro-inverters, but they add >$100 to the cost of each panel. Could I have the professionals install a Sunny Boy 3000-TL with 5 panels now, and then relatively easily (and cheaply) add more panels to the same array later? (I am confident that I am physically capable of doing it, so my question is a technical/electrical one.)

Thank you for your expertise

[silversaver]

Depends on how much larger you add on to exist solar. I assume you have a 3kW inverter and what is the current output/size of your solar array?

[peakbagger]

With a central inverter you need to get the strings voltages within the operating range of the inverter. I will let you look up the specs on you panel but you need to determine the voltage each panel puts out at the coldest and warmest expected panel temps by using the temperature coefficient supplied on the panel spec sheet. Then multiply the voltages by the number of panels. The resulting minimum and maximum voltage has to end up within the operating voltage range of the inverter. What you may have to do if you end up with a voltage over the max is split the array into two strings and then rerun the calculations and hope you still end up in the operating range of the inverter. Ideally you want to end up on the high end of the inverter voltage range. With a 3000 watt inverter I doubt you will need more than 2 strings but if for some reason you end up with three then you need fuses on the strings in the combiner box.

In general microinverters tend to be a bit more user friendly for doing a system expansion but do note at some point you will also need to run a parallel feeder back to the panel. That point is well over 3000 watts

One thing to keep in mind, panels are only on the market for a short time. What is in stock today may be gone tomorrow so you need to buy all the panels in one shot. Even racking designs tend to change so you probably should buy all you racking and mounts.

[Softco]

Thank you for your quick and thorough replies.

The initial install would involve 5 - 250w Canadian Solar panels installed on a 12-12/45deg pitch roof facing exactly south w/ 0 shade. From what I've seen of the calculations (and based on how anxious the installers are to do it) it looks like this inverter would easily support a string of 10-12 panels. I've found a bunch of online calculators, but none that will help me determine how many panels any given inverter will support.

For me the immediate issue is how feasible it is to piggy-back additional panels on the initial string inverter install. From what I can see, the heavy lifting of solar happens with the first install (gov't paperwork, grid tie-in, etc.). If that can be done at a low cost professionally, and then additional panels can be added by me just by racking and adding panels at their actual cost, by my figuring, break even can happen much earlier than the 10 year mark that the professional installers seem to shoot for.

Thank you again for any help you can offer in refining and/or debunking my assumptions.

[russ]

TThe initial install would involve 5 - 250w Canadian Solar panels

For me the immediate issue is how feasible it is to piggy-back additional panels on the initial string inverter install. From what I can see, the heavy lifting of solar happens with the first install (gov't paperwork, grid tie-in, etc.).

In most localities I believe you really are just starting over - forget the piggyback concept.

[Softco]

In most localities I believe you really are just starting over - forget the piggyback concept.

This seems to defy common sense since the professional installers are all too happy to come back later and add more panels @ $1000 each.

[sensij]

This seems to defy common sense since the professional installers are all too happy to come back later and add more panels @ $1000 each.

Well, yeah, they charge a lot because they are essentially starting over. If you have a net metering contract with your Poco, there may be some verbage on how much larger you can go before a new contract needs to be signed. The new agreement may require another round of permitting and inspections for approval. As I understand it, the increase allowed in my locality is 10%, so for a 5 panel system, there is no room to grow without re-engaging in that process.

[russ]

This seems to defy common sense since the professional installers are all too happy to come back later and add more panels @ $1000 each.

with permits and all

[peakbagger]

The other thing to be concerned is a code update. If you add on to a system built to one version of the code and you want to upgrade it you will have to upgrade the entire system to the new code.

[SunEagle]

Again here is someone that thinks they can save a boat load of money without really understanding the legalities of performing electrical work without the proper paperwork and agreements with the POCO.

If a 5 panel system can be installed for "FREE" how big a deal is adding a few more panels up front and having to spend a few thousand dollars when the bulk of the system is paid by someone else?

[Naptown]

Again here is someone that thinks they can save a boat load of money without really understanding the legalities of performing electrical work without the proper paperwork and agreements with the POCO.

If a 5 panel system can be installed for "FREE" how big a deal is adding a few more panels up front and having to spend a few thousand dollars when the bulk of the system is paid by someone else?

I agree
Doubling the number of panels will not double the cost of the system
In your case permitting inspections and inverter costs are the same wether 5 panels or 12 panels.
You should only be paying for the added costs of the panels, racking and labor.

[russ]

I agree
Doubling the number of panels will not double the cost of the system
In your case permitting inspections and inverter costs are the same wether 5 panels or 12 panels.
You should only be paying for the added costs of the panels, racking and labor.

He wants to pay an installer to install a system of possibly 5 panels and later after it is online go back and add 5 more panels on his own if I understand correctly.

[SunEagle]

He wants to pay an installer to install a system of possibly 5 panels and later after it is online go back and add 5 more panels on his own if I understand correctly.

Yup. That way he can save the money that the nasty installer wanted for a bigger system.

[PVAndy]

Yup. That way he can save the money that the nasty installer wanted for a bigger system.

Remember an earlier poster talked about panel voltage. It's actually considerably more complex than that, suffice it to say that to add panels to a string and maintain efficiency you essentially need to use identical (wattage, brand and type ) of panels. The IV curves must match or being a series circuit it will revert to the lowest panel current.

Andy

NABCEP Certified Installation Professional
Solar Design Engineer

[Softco]

Remember an earlier poster talked about panel voltage. It's actually considerably more complex than that, suffice it to say that to add panels to a string and maintain efficiency you essentially need to use identical (wattage, brand and type ) of panels. The IV curves must match or being a series circuit it will revert to the lowest panel current.

Andy

NABCEP Certified Installation Professional
Solar Design Engineer

Thanks Andy!

This is my first post (and day) on this forum and I guess I should have anticipated that it would be populated by people who are on different ends of the solar transaction. I appreciate that some feed their family working in this business, hopefully they can appreciate that for many people solar is uncertain territory, with many stories of bones already left in its wake. I'm content to have a 5-panel system, but how crazy is it to think that a new president could kill the subsidies and make solar no longer a viable business for my installer. At that point, I'm on my own if I want to upgrade my system. So, before I start, I want to understand what wrinkles that scenario would bring.

I appreciate that gov't and poco regs are a huge headache for many. However, I live in a small town that generates its own power. I would be one of <10 people with a grid tie-in in the whole town. I don't believe our poco is sophisticated (or well staffed) enough to monitor the minutia of my contract terms, but I will check to be sure. Another poster mentioned "code" changes. I don't know if that referred to building code or electrical code, but in my area, it's my understanding that the homeowner is given wider latitude to make changes to their own property.

Finding identical panels, to what I have initially installed, at some future date is a legitimate concern with a string inverter. I guess worst-case, you replace the original five, too. The remainder of the original install should still make the upgrade easier. Perhaps, this is another argument for the micro-inverter route. If I do end up on my own in the future, maybe by that time micro-inverters will be more reliable and price-competitive.

I thank you for your considered responses - and even the flames. Getting this right is worth it.